Resin-coated metal sheet for can lids

Abstract

A resin-coated metal sheet for can lids includes a metal sheet coated with thermoplastic resin films on both surfaces and formed into a can lid. A thermoplastic resin film A based on polybutylene terephthalate (PBT) and polyethylene terephthalate (PET) is heat-fused on a surface of the metal sheet serving as an exterior surface of the can lid, and a thermoplastic resin film B based on polyethylene terephthalate (PET) is heat-fused on a surface of the metal sheet serving as an interior surface of the can lid. A composition ratio (wt %) of PBT/PET in the thermoplastic resin film A on the exterior surface is (PBT/PET)=(40/60) to (80/20), and the thermoplastic resin film B on the interior surface includes 95 mol % or more of PET.

The invention claimed is: 
     
       1. A resin-coated metal sheet for can lids, the resin-coated metal sheet comprising a metal sheet coated with thermoplastic resin films on both surfaces and formed into a can lid, wherein
 a thermoplastic resin film A based on polybutylene terephthalate (PBT) and polyethylene terephthalate (PET) is heat-fused on a surface of the metal sheet serving as an exterior surface of the can lid, and a thermoplastic resin film B based on polyethylene terephthalate (PET) is heat-fused on a surface of the metal sheet serving as an interior surface of the can lid, 
 a composition ratio (wt %) of PBT/PET in the thermoplastic resin film A on the exterior surface is (PBT/PET)=(40/60) to (80/20), and the thermoplastic resin film B on the interior surface includes 95 mol % or more of PET, 
 a melting point derived from PET of the thermoplastic resin film B on the interior surface is 250° C. or higher and 265° C. or lower and is higher than a melting point derived from PBT in the thermoplastic resin film A on the exterior surface by 25° C. or more, 
 in the thermoplastic resin film A on the exterior surface, a Raman band intensity ratio (I 90 /I 0 ) between Raman band intensity (I 0 ) of 1615±10 cm −1  that is measured on a polarization plane horizontal to the surface by laser Raman spectroscopy and Raman band intensity (I 90 ) of 1615±10 cm −1  that is measured on a polarization plane vertical to the surface by laser Raman spectroscopy is 0.60 or more, and in the thermoplastic resin film B on the interior surface, half-width of Raman band of 1730±10 cm −1  that is measured on a polarization plane horizontal to the surface by laser Raman spectroscopy is 15 to 20 cm −1 .